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Mon, 21 Sep 2026 12:27:36 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 21 Sep 2026 19:27:36 +0000 Message-Id: To: "Eduard Zingerman" , "Vineet Gupta" Cc: "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "Ihor Solodrai" , "John Fastabend" , "Shuah Khan" , "bpf" , "LKML" , "open list:KERNEL SELFTEST FRAMEWORK" Subject: Re: [PATCH bpf-next v2 03/13] bpf: track low-32 scalar equality across zero-extending movs From: "Alexei Starovoitov" X-Mailer: aerc 0.17.0 References: <20260910164635.459558-1-vineet.gupta@linux.dev> <20260910164635.459558-4-vineet.gupta@linux.dev> <4ab75099-0e95-4fee-81da-6f4198e3e6a0@linux.dev> <202c45e2-58ba-4ad5-a234-c90703031f91@linux.dev> In-Reply-To: On Mon Sep 21, 2026 at 7:10 PM UTC, Eduard Zingerman wrote: > On Mon, 2026-09-21 at 18:59 +0000, Alexei Starovoitov wrote: > > On Mon Sep 21, 2026 at 5:28 PM UTC, Eduard Zingerman wrote: > > > On Wed, 2026-09-16 at 17:30 -0700, Alexei Starovoitov wrote: > > > > On Wed, Sep 16, 2026 at 5:08=E2=80=AFPM Vineet Gupta wrote: > > > > >=20 > > > > > It ended up with full testsuite run parity - after 4 incremental = patches. > > > > > But the pattern of all those patches was adding some predicate / > > > > > special-casing to reg->add_const > > > > >=20 > > > > > hunk 1 > > > > >=20 > > > > > - if (src_reg->add_const) > > > > > + if (src_reg->add_const && src_reg->delta) > > > >=20 > > > > why? It should not. > > > > My point is that zero is not special. > > > > It should be handled within the current framework. > > > > All these extra hunks are not correct. > > > > ADD_CONST_32 logic should work for delta =3D=3D 0 just like > > > > it works for delta =3D=3D 1. > > >=20 > > > After thinking about it some more, I agree that having an orthogonal > > > encoding would be nice. However, it appears that the split should be > > > somewhat different: > > >=20 > > > struct bpf_reg_state { > > > ... > > > s32 delta; > > > u32 id; > > > enum id_link_kind { full, zext, sext } link_kind; > > > ... > > > } > > >=20 > > > Where: > > > - id =3D=3D 0 =3D> no id link > > > - full =3D> all 64-bits of the register are identical to > > > all 64-bits of a scalar value `id' (let's call it X). > > > =E2=88=80 rA{.id =3D=3D X, .link =3D=3D full}, rB{X,full} = =3D> rA =3D=3D rB > > > - zext =3D> lower 32-bits of the register are identical to > > > lower 32-bits of a scalar value X, > > > upper 32-bits of the register are null. > > > =E2=88=80 rA{.id =3D=3D X, .link =3D=3D ?}, rB{X,zext} =3D>= rA % 32 =3D=3D rB % 32 > > > - sext =3D> lower 32-bits of the register are identical to > > > lower 32-bits of a scalar value X, > > > upper 32-bits of the register are either 0 or 1, > > > depending on the bit 31 value. > > > =E2=88=80 rA{.id =3D=3D X, .link =3D=3D ?}, rB{X,sext} =3D>= sext(rA % 32) =3D=3D sext(rB % 32) > >=20 > > hmm. > > there is also 32-bit link with delta, right? > > My point is that delta is independent of 32-bit/64-bit property. > `delta' can be used to propagate in both directions: > - full 64 bit -> 32 bit sign/zero-extened > - 32 bit sign/zero-extened -> full 64-bit both? how ? I was under impression that in 32-bit domain delta is one way. rX =3D ... wY =3D wX wY +=3D 5 if wY =3D=3D 10 We cannot do -5 to rX and we cannot use your above 'full' encoding for wY +=3D 5. Currently we use BPF_ADD_CONST32 for wY +=3D 5 I don't see how 'full' can work.